1. Field of the Invention
The present invention relates to a liquid crystal display device capable of displaying stereoscopic three-dimensional images which is used for TV sets, game machines, personal computers, CAD apparatus, medical monitors, portable information terminals, and the like.
2. Description of the Related Art
It has been long attempted to reproduce stereoscopic images or three-dimensional images. A variety of methods have been proposed to realize this goal, including a method using a laser hologram and the like. Among these methods, two types of three-dimensional image display methods with higher perfection which can display full-color moving pictures of three principal colors have been proposed. These two types are based on the same principle: That is, different images for the right and left eyes of an observer are separately displayed, to generate the parallax between the two eyes by the image deviation between the two eyes, and thus to provide the observer with the sense of depth in the images.
The first one of the two methods is a polarizing glasses method. In this method, images for the right and left eyes include two types of linearly polarized light in which polarizing directions are inclined at an angle of 90.degree. from each other. The observer perceives three-dimensional images by wearing a pair of polarizing glasses. In the case of projection display, images for right and left eyes are superimposed with each other on a screen using two polarizing projectors. In the case of direct-view display, images output from two display devices are synthesized by a half mirror or a polarizing mirror.
The second one of the two methods is a shutter glasses method. In this method, images for right and left eyes are displayed by a single display device using time division. The observer wears a pair of glasses having a shutter function which alternately opens and closes in synchronization with the displayed images so as to provide three-dimensional images. This method is applicable to both the projection display and the direct-view display.
In the above two methods, images for right and left eyes are both presented as two-dimensional images. These two-dimensional images may be displayed by a liquid crystal display (LCD), cathode ray tube (CRT), a plasma display, or the like depending on the use of the images.
The polarizing glasses method requires two display devices and a projection device since two images having different polarizing axes must be simultaneously displayed at any time. This increases the cost and the size of the entire apparatus, and thus is not suitable for domestic use.
In order to overcome the above problem of the polarizing glasses method, Japanese Laid-Open Publication No. 58-184929, for example, proposes a method for displaying three-dimensional images by use of a single display device. According to this method, a mosaic polarizing layer composed of a plurality of portions corresponding to pixels arranged in a mosaic shape where the polarizing axes of adjacent portions are perpendicular to each other is closely attached to the outer surface of the display device (CRT or LCD). The observer can perceive three-dimensional images by observing two-dimensional images for the right and left eyes presented by the display device via a pair of polarizing glasses. The above publication, however, discloses no practical description on the position of the mosaic polarizing layer in the display device when the display device is an LCD. Hereinbelow, therefore, the method disclosed in the above publication will be described assuming that the polarizing layer is disposed on the outer surface of a liquid crystal display device.
FIG. 13 is a conceptual view of a liquid crystal display device having a three-dimensional display function proposed in Japanese Laid-Open Publication No. 58-184929 mentioned above.
A display device body 701 includes right-eye pixels 706 and left-eye pixels 707 for displaying images for the right and left eyes, respectively. The right-eye and left-eye pixels 706 and 707 constitute a display screen. Two types of polarizing layers 703 and 704 of which polarizing axes are perpendicular to each other are disposed alternately on the front side of the display screen. More specifically, the polarizing layers 703 and 704 are disposed so as to correspond to the right-eye pixels 706 and the left-eye pixels 707, respectively, to distinguish images for the right eye and the left eye from each other. The observer wears a pair of polarizing glasses 712 which include a right-eye polarizing plate 712b of which polarizing axis is identical to that of the polarizing layers 703 disposed in front of the right-eye pixels 706 and a left-eye polarizing plate 712a of which polarizing axis is identical to that of the polarizing layers 704 disposed in front of the left-eye pixels 707. By wearing the pair of glasses 712, the right and left eyes of the observer observe only images for the right and left eyes, respectively, and thus perceives stereoscopic three-dimensional images.
The display device body 701 includes a pair of glass substrates 702a and 702b disposed to sandwich a liquid crystal layer 705 therebetween. The right-eye pixels 706 and the left-eye pixels 707 are formed on the surface of one of the glass substrates, i.e., the glass substrate 702a (located left as is viewed in FIG. 13), facing the liquid crystal layer 705. An alignment film 710a is formed on the right-eye and left-eye pixels 706 and 707. A polarizing plate 708 is disposed on the surface of the glass substrate 702a opposite to the surface thereof facing the liquid crystal layer 705. A transparent electrode 709 and an alignment film 710b are formed in this order on the surface of the other glass substrate, i.e., the glass substrate 702b, facing the liquid crystal layer 705. The liquid crystal layer 705 is sealed with a sealing member 711 formed to surround the liquid crystal layer 705.
The conventional display device with the above configuration has the following problem.
Referring to FIG. 14, in the display device body 701, the glass substrate 702b exists between the right-eye and left-eye pixels 706 and 707 and the right-eye and left-eye polarizing layers 703 and 704. When the observer observes the display screen from the front position as is shown by the dash-dot lines in FIG. 14, the observer can perceive normal three-dimensional images. However, as the eyes of the observer move upward or downward from the front position, the right-eye pixels 706 may be observed via the polarizing layers 704 for the left eye and, reversely, the left-eye pixels 707 may be observed via the polarizing layers 703 for the right eye, as is shown by the dotted lines in FIG. 14. In such a case, a phenomenon called crosstalk may be generated in which some images for right and left eyes are observed by the reverse eyes, and thus actual three-dimensional images may not be obtained. In FIG. 14, some components of the display device body 701 shown in FIG. 13 are omitted for simplification.
In order to eliminate such crosstalk, Japanese Laid-Open Publication No. 62-135810 proposes a display device including a single transparent liquid crystal display element. In this proposed display device, polarizing layers in which the polarizing directions are different from each other are disposed inside a pair of glass substrates of the transparent liquid crystal display element. With this configuration, right-eye pixels and left-eye pixels of the transparent liquid crystal display element are adjacent to the polarizing layers for the right eye and the polarizing layers for the left eye, respectively. This prevents the generation of crosstalk as described above even when the eyes of the observer move upward or downward from the front position of the display screen. As a result, the range within which three-dimensional images can be perceived is not limited, and thus a display device capable of displaying three-dimensional images with a wide viewing angle can be obtained.
A transmission liquid crystal display element is conventionally used for such a liquid crystal display device which has the three-dimensional display function and employs the polarizing glasses method. This type of device requires a light source for illuminating the liquid crystal display element, i.e., a backlight, increasing power consumption. In the applications using a battery, such as portable information terminals, this light source requirement shortens the time duration available from one charging of a battery. Providing a light source also increases the production cost of the display device.
In view of the foregoing, the objective of the present invention is to provide a thin and light-weight liquid crystal display device with the three-dimensional display function which has a prolonged time duration with reduced power consumption, can be manufactured at low cost, and eliminates the generation of crosstalk at the display of three-dimensional images to realize good image display with a wide viewing angle and thus to expand the applicable field of view of the device.